US authorities erred badly in probing a disastrous gun-running operation into Mexico, a government inspector said Wednesday in a report that nonetheless cleared Attorney General Eric Holder.

The 2009-2010 operation was named Fast and Furious, after the series of Hollywood action movies, and its aim was to track weapons purchased by bogus buyers in Arizona and smuggled to drug cartels in Mexico.

But many of the guns went missing, and two were later found at the murder scene of a US border patrol agent.

Back in June the Republican-controlled House of Representatives took the historic and controversial step of holding Holder in contempt over the gun-tracking operation and his refusal to turn over requested documents.

It wanted to know if there was a cover up of the operation, but the Obama administration cited "executive privilege" in declaring the documents protected.

The report released Wednesday by the Justice Department's inspector general Michael Horowitz "details a pattern of serious failures" by the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) and the US Attorney's office for the district of Arizona in their investigation of what went wrong in Fast and Furious.

But the inspector said he found "no evidence that Attorney General Holder was informed about Operation Fast and Furious, or learned about the tactics employed by ATF in the investigation, prior to January 31, 2011."

Still, Horowitz was scathing with those who did run the operation.

"Operation Fast and Furious received little or no supervision by ATF Headquarters, despite its connection to a dangerous narcotics cartel in Mexico, the serious risk it created to public safety in the United States and Mexico, and its potential impact on the country's relationship with Mexico," the report stated.

Authorities in the ATF and the US attorney's office in Arizona who designed, implemented or supervised Fast and Furious will be reviewed and possibly punished, Holder said in a statement after the inspector's report came out.

He also accepted the resignation of a deputy assistant attorney general.